Electric compressor

ABSTRACT

There is provided an electric compressor includes a compression mechanism, an electric motor, a motor housing having an injection port that communicates with one of compression chambers that is in the middle of the compression, a discharge housing having a discharge chamber into which compressed refrigerant is discharge, and an intermediate pressure housing disposed between the motor housing and the discharge housing. The intermediate pressure housing has an introduction port for introducing intermediate pressure refrigerant from an external refrigerant circuit and a communication passage between the introduction port and the injection port of the motor housing. The introduction port and the communication passage cooperate with the injection port to allow the intermediate pressure refrigerant to be injected into the compression chamber. The communication passage has in the middle thereof a muffler chamber. A partition member separates the muffler chamber and the discharge chamber.

BACKGROUND OF THE INVENTION

The present invention relates generally to an electric compressor and specifically to an electric compressor with an injection mechanism.

Japanese Patent Application Publication No. H08-303361 discloses a scroll type compressor including a power save mechanism that controls the displacement of the compressor by allowing refrigerant gas being compressed to flow to low pressure region of the compressor through a bypass passage. The power save mechanism has a cover plate on the upper surface of an end plate of a fixed scroll member of the compressor. The cover plate has therein a backpressure passage in which high pressure refrigerant gas and low pressure gas from a unit circuit are supplied selectively through a high pressure guide tube and a bypass passage that is in communication with the backpressure passage. The end plate of the fixed scroll member has therethrough a first save hole and a second save hole that are in communication with a compression chamber and a return hole that is in communication with a low pressure chamber. The first save hole, the second save hole, and the return hole are communicable with the bypass passage through a first save valve, a second save valve, and a valve body that are provided at the openings of the respective holes adjacent to the bypass passage. The first save valve, the second valve, and the valve body can be opened and closed in response to the pressure of the refrigerant gas supplied into the bypass passage.

According to the pressure of the refrigerant gas supplied into the bypass passage through the backpressure passage from the high pressure guide tube, the opening and closing of the first save valve, the second valve, and the valve body are controlled. When high pressure refrigerant gas is supplied into the bypass passage from the high pressure guide tube through the backpressure passage, the first save valve, the second valve, and the valve body are moved in the directions that close the first save hole, the second save hole, and the return hole, respectively. When low pressure refrigerant gas is supplied into the bypass passage from the high pressure guide tube through the backpressure passage, the first save valve, the second save valve, and the valve body are moved in the directions that open the first save hole, the second save hole, and the return hole, respectively.

In the scroll type compressor according to the above-cited Publication, the bypass passage needs to be extended for the pressure of refrigerant gas supplied into the bypass passage from the high pressure guide tube through the backpressure passage to be stable. Though the thickness of the cover plate needs to be increased for extending the bypass passage, there is no space between the end cap of the compressor and the cover plate that is large enough for extending the bypass passage adequately. If the bypass passage is extended, the space for the discharge chamber formed between the end cap and the cover plate is decreased.

The present invention, which has been made in light to the above problems, is directed to providing an electric compressor that can easily increase the volume of its injection chamber and efficiently decrease the pressure pulsation of intermediate pressure refrigerant introduced into the injection chamber.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, there is provided an electric compressor includes a compression mechanism having a plurality of compression chambers, an electric motor driving the compression mechanism to draw refrigerant into the compression chambers and compress the refrigerant in the compression chambers, a motor housing accommodating the electric motor and the compression mechanism, the motor housing having an injection port that communicates with one of the compression chambers that is in the middle of the compression, a discharge housing having a discharge chamber into which the compressed refrigerant is discharge, and an intermediate pressure housing disposed between the motor housing and the discharge housing. The intermediate pressure housing has an introduction port for introducing intermediate pressure refrigerant from an external refrigerant circuit and a communication passage that provides communication between the introduction port and the injection port of the motor housing. The introduction port and the communication passage cooperate with the injection port to allow the intermediate pressure refrigerant to be injected into the compression chamber. The communication passage has in the middle thereof a muffler chamber whose volume is large than volume of the communication passage other than the muffler chamber. Pressure of the intermediate pressure refrigerant is higher than pressure of the drawn refrigerant and lower than pressure of the compressed refrigerant discharged into the discharge chamber. A partition member separates the muffler chamber and the discharge chamber.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of an electric compressor according to an embodiment of the present invention;

FIG. 2 is a sectional view taken along the line A-A of FIG. 1;

FIG. 3 is an enlarged sectional view of a valve block of the electric compressor of FIG. 1;

FIG. 4 is a sectional view taken along the line B-B of FIG. 1;

FIG. 5 is a sectional view taken along the line C-C of FIG. 1;

FIG. 6 is a perspective view of a partition member of the electric compressor of FIG. 1;

FIG. 7 is a longitudinal sectional view showing a state where the partition member is mounted in the electric compressor of FIG. 1; and

FIG. 8 is a longitudinal sectional view showing a state where a partition member of an electric compressor according to another embodiment of the present invention is mounted.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following will describe an electric compressor of an embodiment according to the present invention with reference to FIGS. 1 through 8. The electric compressor of the present embodiment is a scroll type electric compressor that is mounted on an electric vehicle (hereinafter referred to merely as the electric compressor). The electric compressor forms a part of the refrigerant circuit of a vehicle air-conditioner.

Referring to FIG. 1, the electric compressor that is designated by numeral 10 integrally includes a compression mechanism 11 compressing refrigerant as fluid and an electric motor 12 for driving the compression mechanism 11. The electric compressor 10 further includes a housing assembly 13 that is made of metal. In the present embodiment, the housing assembly 13 is made of an aluminum alloy. The housing assembly 13 includes a motor housing 14, a valve block 15, and a discharge housing 16. The valve block 15 forms a part of an outer shell of the housing assembly 13. It is noted that the valve block 15 corresponds to the intermediate pressure housing of the present invention. The motor housing 14, the valve block 15, and the discharge housing 16 are connected together by bolts 17.

The motor housing 14 has at the end thereof that is adjacent to the valve block 15 a plurality of bolt holes 53 that extend parallel to the axial direction of the electric compressor 10 and are spaced at an interval in the circumferential direction of the motor housing 14. The bolt 17 is inserted in the bolt hole 53 and screwed, so that the motor housing 14, the valve block 15, and the discharge housing 16 are fastened together. It is noted that the bolt hole 53 corresponds to the bolt fastening hole of the present invention. Specifically, a plurality of sets of holes 61, 57 and 53 is formed in the discharge housing 16, the valve block 15 and the motor housing 14, respectively, in axial direction of the electric compressor 10 at positions that are spaced at an interval in the circumferential direction of the housing assembly 13. Each bolt 17 is inserted through the holes 61, 57 and screwed into the bolt hole 53 thereby to fasten the motor housing 14, the valve block 15, and the discharge housing 16 together. The holes 53, 57, 61 correspond to the bolt fastening holes of the present invention.

The motor housing 14 of the electric compressor 10 has therein the compression mechanism 11 and the electric motor 12. The compression mechanism 11 includes a fixed scroll member 18 and a movable scroll member 19. A compression chamber 20 is formed by the fixed scroll member 18 and the movable scroll member 19. The motor housing 14 has therethrough an inlet port 21. The inlet port 21 is connected to an external refrigerant circuit (not shown in the drawing). Low pressure refrigerant is flowed from the external refrigerant circuit through the inlet port 21 into the motor housing 14 during the operation of the electric compressor 10.

A shaft support member 22 is provided in the motor housing 14 between the fixed scroll member 18 and the electric motor 12. The shaft support member 22 forms a part of the compression mechanism 11 and has therein a bearing 24 that supports one end of a rotary shaft 23 of the electric motor 12. The other end of the rotary shaft 23 is supported by the motor housing 14 through a bearing 25. The shaft support member 22 has therethrough a suction port 26 that provides fluid communication between the interior of the motor housing 14 and the compression chamber 20. The refrigerant drawn into the motor housing 14 through the inlet port 21 is introduced through the suction port 26 into the compression chamber 20. The shaft support member 22 has fixed pins 27 press-fitted in the holes formed in the shaft support member 22 and extending toward the movable scroll member 19.

The rotary shaft 23 has at one end thereof adjacent to the fixed scroll member 18 an eccentric pin 28 extending from the end toward the fixed scroll member 18. The axis Q of the eccentric pin 28 is offset from the axis P of the rotary shaft 23. When the rotary shaft 23 rotates, the eccentric pin 28 is rotated eccentrically with respect to the axis P of the rotary shaft 23. A drive bush 29 is relatively rotatably mounted on the eccentric pin 28. The drive bush 29 has a balancing weight that balances the eccentric load of the eccentric pin 28 and the drive bush 29 developed by the rotation of the rotary shaft 23.

The movable scroll member 19 is rotatably mounted on the drive bush 29 through a bearing 30, so that the movable scroll member 19 can make an orbital motion with the rotation of the rotary shaft 23. The movable scroll member 19 includes a circular movable base plate 31 and a movable scroll wall 32. The movable scroll member 19 is disposed such that the surface of the movable base plate 31 extends perpendicularly to the axis P. The movable scroll wall 32 is formed extending from the surface of the movable base plate 31 on the side thereof that is adjacent to the fixed scroll member 18.

As shown in FIG. 1, a plurality of bottomed cylindrical holes 33 is formed in the movable base plate 31 of the movable scroll member 19 at positions adjacent to the outer peripheral edge of the movable base plate 31. A plurality of anti-rotation rings 34 is inserted in the respective bottomed cylindrical holes 33.

The fixed pins 27 are located at positions in the shaft support member 22 that correspond to the respective bottomed cylindrical holes 33. Each fixed pin 27 extends from the shaft support member 22 toward the bottomed cylindrical hole 33 and is inserted into the anti-rotation ring 34. In the present embodiment, the anti-rotation ring 34 and the fixed pins 27 form the anti-rotation mechanism for preventing the movable scroll member 19 from rotating on its axis. Therefore, the movable scroll member 19 orbits around the axis P without rotating on its axis with the rotation of the rotary shaft 23. That is, the movable scroll member 19 is provided so as to make an orbital movement around the axis P without rotation.

The fixed scroll member 18 is engaged with the movable scroll member 19 in facing relation to each other and fixed to the motor housing 14. The fixed scroll member 18 has a circular fixed base plate 35 and a fixed scroll wall 36. The fixed base plate 35 and the fixed scroll wall 36 of the fixed scroll member 18 are integrally formed. The fixed base plate 35 is disposed in the motor housing 14 so as to close the end of the motor housing 14. The fixed scroll wall 36 is formed extending from the surface of the fixed base plate 35 on the side thereof that is adjacent to the movable scroll member 19. The fixed base plate 35 forms a part of the motor housing 14.

In the electric compressor 10 according to the present embodiment, the compression chambers 20 are formed between the fixed scroll member 18 and the movable scroll member 19 by the contact engagement of the fixed scroll wall 36 of the fixed scroll member 18 and the movable scroll wall 32 of the movable scroll 19. As shown in FIG. 2, two compression chambers 20 of the same volume and pressure are formed simultaneously. Refrigerant is introduced through the suction port 26 into two compression chambers 20 formed at positions adjacent to the outer periphery of the electric compressor 10. The orbiting motion of the movable scroll member 19 causes the two compression chambers 20 to move toward the center, so that the volume of the compression chambers 20 is decreased and the refrigerant in the compression chambers 20 is compressed. The fixed scroll member 18 has at the center thereof a discharge port 37 having a discharge valve 38 that opens and closes the discharge port 37 and a retainer 56 that regulates the opening of the discharge valve 38. The discharge valve 38 is opened when the pressure of the refrigerant compressed in the compression chambers 20 becomes greater than a predetermined pressure.

As shown in FIGS. 1 and 2, the fixed base plate 35 of the fixed scroll member 18 has therein two injection ports 39 that are formed radially outward of the discharge port 37 in communication with the compression chambers 20 that are then in the middle of compression, and have an opening at a position adjacent to the valve block 15. The injection port 39 is a passage through which intermediate pressure refrigerant is introduced into the compression chamber 20. The injection ports 39 are formed in communication with the compression chambers 20 that are then in the phase of compression. The diameter of the injection port 39 adjacent to the movable scroll member 19 is smaller than that of the injection port 39 adjacent to the valve block 15, so that intermediate pressure refrigerant in the injection port 39 is injected into the compression chamber 20. The small diameter portion of the injection port 39 serves as a nozzle.

The electric motor 12 includes a stator 40 fixed on the inner peripheral surface of the motor housing 14 and a rotor 41 fixed on the rotary shaft 23. The electric compressor 10 has a drive circuit case 65 connected to the motor housing 14. The drive circuit case 65 has therein a drive circuit 64 that drives the electric motor 12. Three-phase AC power is supplied from the drive circuit 64 to a coil 40A of the stator 40 and the rotor 41 is rotationally driven by power supplied to the coil 40A of the stator 40 and the rotor 41 is driven to rotate, accordingly. With the rotation of the rotor 41, the compression mechanism 11 that is operatively connected to the rotary shaft 23 is operated for compression of refrigerant.

As shown in FIGS. 1 and 3, the valve block 15 has a cylindrical shape and a predetermined thickness in the axial direction of the rotary shaft 23. The valve block 15 is made of an aluminum alloy. As shown in FIG. 3, the valve block 15 has a front surface 7 facing the motor housing 14, a rear surface 8 facing the discharge housing 16, and a peripheral wall 9 formed between the front surface 7 and the rear surface 8. As shown in FIGS. 3 and 4, the valve block 15 has in the center thereof a rectangular recess 42 that is recessed in the radial direction of the rotary shaft 23 and has an opening adjacent to the discharge housing 16. A step portion 43 is formed in the recess 42 at a position adjacent to the bottom of the recess 42. A muffler chamber 45 (injection chamber) is formed by closing the opening of the recess 42 by a partition member 44. The muffler chamber 45 serves as a muffler that reduces the pressure pulsation of the intermediate pressure refrigerant introduced into the muffler chamber 45. It is noted that the partition member 44 will be described in detail later.

As shown in FIG. 3, the muffler chamber 45 has therein a check valve 46. The check valve 46 is formed by a valve plate 47 having a hole 47A, a reed valve 48 disposed so as to cover the hole 47A, and a retainer 49 regulating the opening of the reed valve 48. The check valve 46 is fastened to the step portion 43 by bolts 50. The muffler chamber 45 is divided into two spaces by the check valve 46, namely the space S1 on the discharge housing 16 side of the check valve 46 and the space S2 on the motor housing 14 side of the check valve 46.

The valve block 15 has therein an introduction port 51 that is in communication with the space S1 of the muffler chamber 45 and has an opening at the outer periphery of the valve block 15. The introduction port 51 serves as a passage through which intermediate pressure refrigerant is introduced from an eternal refrigerant circuit (not shown in the drawing). The intermediate pressure refrigerant introduced through the introduction port 51 is flowed into the muffler chamber 45. The external refrigerant circuit includes an evaporator and a condenser and a part of the refrigerant having intermediate pressure decompressed between the evaporator and the condenser and having an intermediate pressure is introduced through a high pressure guide tube (not shown in the drawing) into the introduction port 51. Intermediate pressure refrigerant refers to refrigerant whose pressure is higher than suction pressure of refrigerant drawn at the inlet port 21 and lower than discharge pressure of refrigerant at the discharge port 37.

The valve block 15 has therein two supply ports 52 that are formed between the bottom surface of the recess 42 and the front surface 7 of the valve block 15 in communication with the respective injection ports 39 formed in the fixed scroll member 18 and also with the space S2 of the muffler chamber 45. When intermediate pressure refrigerant is introduced through the introduction port 51 into the space S1 of the muffler chamber 45, the reed valve 48 is bent to open by the pressure of the refrigerant. Accordingly, the intermediate pressure refrigerant in the space S1 of the muffler chamber 45 is supplied through the space S2 of the muffler chamber 45, the supply port 52, and the injection port 39 into the compression chamber 20. Then, the intermediate pressure of refrigerant is higher than the pressure of the compression chamber 20 into which the intermediate pressure refrigerant is to be supplied. The introduction port 51, the muffler chamber 45 (51, S2), and the supply port 52 cooperate to form a communication passage through which the introduction port 51 is in communication with the injection port 39. The muffler chamber 45 is provided in the middle of the communication passage and formed as an expanded space.

A recess 66 is formed in the valve block 15 on the side thereof opposite from the muffler chamber 45 and has an opening at the end adjacent to the discharge port 37 and a discharge valve chamber 55 is formed by closing the recess 66 of the valve block 15 covered by the fixed scroll member 18. The discharge valve chamber 55 has therein the discharge valve 38 and the retainer 56 for the discharge port 37. The valve block 15 has therein a passage 6 (refer to FIG. 1) through which the discharge valve chamber 55 is in communication with the discharge chamber 58.

Thus, the introduction port 51, the muffler chamber 45, the check valve 46, and the supply port 52 are all formed in the valve block 15. The introduction port 51, the muffler chamber 45, the check valve 46, and the supply port 52 cooperate to form the injection mechanism. The injection mechanism serves as a mechanism that allows the refrigerant of an intermediate pressure that is higher than the suction pressure and lower than the discharge pressure of refrigerant to be introduced into the compression chamber 20 that is then in the middle of compression.

As shown in FIGS. 1 and 5, the discharge housing 16 has therein a circular recess 62 that is opened toward the valve block 15. A projection 73 is formed extending from the bottom of the recess 62 toward the valve block 15. The recess 62 of the discharge housing 16 is closed the valve block 15, thereby forming a space that corresponds to the discharge chamber 58. The discharge housing 16 has therein a discharge port 60 that is formed at a position adjacent to the bottom of the recess 62 and opened at the outer periphery of the discharge housing 16. The discharge port 60 has an outlet port 59 at the outer periphery of the discharge port 60. The outlet port 59 is connected to the external refrigerant circuit (not shown in the drawing). The discharge housing 16 further has therein a communication passage 74 that is formed in the center of the projection 73 and through which the discharge chamber 58 is in communication with the discharge port 60. The communication passage 74 is formed parallel to the axial direction of the rotary shaft 23. The discharge housing 16 has therein a hole 61 that is disposed at a position adjacent to the outer periphery of the discharge housing 16 and through which the bolt 17 is inserted parallel to the axial direction of the rotary shaft 23. The plural holes 61 are equally spaced in the circumferential direction of the discharge housing 16. The holes 61 are formed at the same position in the circumferential direction of the discharge housing 16 as the bolt holes 53 formed at the end of the motor housing 14. It is noted that the hole 61 corresponds to the bolt fastening hole.

As shown in FIGS. 1 and 3, the partition member 44 is provided between the valve block 15 and the discharge housing 16. Connecting the valve block 15 and the discharge housing 16 through the partition member 44 forms the discharge chamber 58 and the muffler chamber 45 separately. That is, the partition member 44 has a function that partitions between the discharge chamber 58 and the muffler chamber 45. The muffler chamber 45 is located on the opposite side of the partition member 44 from a part of the discharge chamber 58. It is noted that the two-dot chain line designated by 75 in FIG. 3 shows a plate-shaped partition member according to the prior art.

Referring to FIGS. 6 and 7, the partition member 44 is generally of a box shape and includes bottom portions 67, 68, and a side wall portion 69 that forms the periphery of the partition member 44. The side wall portion 69 is formed extending axially from the bottom portions 67, 68 toward the valve block 15 and surrounded by the discharge chamber 58. A step 77 is formed between the bottom portions 67, 68. In the partition member 44, the bottom portions 67, 68 and the side wall portion 69 are formed extending into the discharge housing 16. As shown FIG. 3, the distance L1 between the rear surface 8 of the valve block 15 and the outer surface of the bottom portion 67 is larger than the distance L2 between the rear surface 8 and the outer surface of the bottom portion 68. The bottom portion 68 has therein an arcuate recess 71. The recess 71 includes a flat bottom portion 71A and a wall portion 71B formed around the bottom portion 71A. A space S3 is formed surrounded by the bottom portions 67, 68, the step 77, and the side wall portion 69 and in communication with the space S1 of the muffler chamber 45. That is, a part of the space S1 of the muffler chamber 45 is formed extending into the discharge housing 16.

The side wall portion 69 of the partition member 44 is formed surrounded by the discharge chamber 58, which increases the volume of the space S1 of the muffler chamber 45. The partition member 44 is made of an aluminum alloy. The partition member 44 has three mounting holes 70 that are disposed on the periphery of the partition member 44. The partition member 44 is fixed on the valve block 15 by bolts 54 that are inserted through the mounting holes 70.

As shown in FIGS. 3 and 4, the valve block 15 has therein a recess 72 that is formed on the valve block 15 side of the discharge housing 16 at a position radially outward of the muffler chamber 45 so as to partially surround the recess 42 and opened to the discharge housing 16. The recess 72 of the valve block 15 that is surrounded by the discharge housing 16, as shown in FIG. 7 is in direct communication with the discharge chamber 58 and forms a part of the discharge chamber 58. That is, the recess 72 serves to expand the volume of the discharge chamber 58.

Referring to FIG. 7, the partition member 44 is disposed in such a way that the recess 71 in the bottom portion 68 of the partition member 44 covers a projection side opening 74A of the communication passage 74 that is located remote from the discharge port 60 so that a clearance is formed between the end of the projection 73 and the surface of the bottom portion 71A of the recess 71 and also a clearance is formed between the outer peripheral surface 73A of the projection 73 and the wall portion 71B. Thus, the discharge passage extending from the discharge chamber 58 to the communication passage 74 is restricted between the projection 73 and the surface of the bottom portion 71A of the recess 71. Adjusting the depth of the recess 71 (or the clearance between the end of the projection side opening 74A and the bottom portion 71A of the recess 71) enables to change the restriction of the discharge passage. The high pressure refrigerant discharged into the discharge chamber 58 is flowed through the restricted passage and the communication passage 74 into the discharge port 60 and discharged through the outlet port 59 into the external refrigerant circuit.

For assembling the electric compressor 10, the valve block 15 having incorporated therein the injection mechanism is prepared, the valve block 15 is set so as to form a part of the housing assembly 13, and the valve block 15, the motor housing 14, and the discharge housing 16 are bolted together. That is, the valve block 15 may be disposed between the motor housing 14 and the discharge housing 16 and integrally fixed by the bolts 17.

The following will describe the operation of the electric compressor 10 having the above-described configuration. The rotary shaft 23 is driven to rotate by the electric motor 12 that is driven by the drive circuit 64. The rotation of the rotary shaft 23 is transmitted through the eccentric pin 28 and the drive bush 29 to the movable scroll member 19 of the compression mechanism 11. The movable scroll member 19 performs an orbital movement around the P without rotation on its own axis by virtue of the anti-rotation ring 34 and the fixed pin 27 that serve as the anti-rotation mechanism. The movable scroll member 19 performs an orbital movement around the axis P without rotation, so that the compression chamber 20 formed between the movable scroll member 19 and the fixed scroll member 18 is moved toward the center and the volume of the compression chamber 20 is decreased, accordingly.

Therefore, refrigerant is flowed through the inlet port 21 into the motor housing 14 and introduced through the suction port 26 into the compression chamber 20. The pressure of the refrigerant is increased with the volume decrease of the compression chamber 20. The high pressure refrigerant opens the discharge valve 38 and is discharged through the discharge port 37 into the discharge valve chamber 55. Then, the refrigerant is flowed through the discharge valve chamber 55 into the discharge chamber 58.

Intermediate pressure refrigerant which is introduced from the external refrigerant circuit through the introduction port 51 into the space S1 of the muffler chamber 45 pushes open the reed valve 48. Accordingly, the refrigerant in the space S1 of the muffler chamber 45 is supplied through the space S2 of the muffler chamber 45, the supply port 52, and the injection port 39 into the compression chamber 20 that is then in the middle of compression. Then, the pressure of the refrigerant in the compression chamber 20 in the middle of compression is lower than that of the intermediate pressure refrigerant.

Supplying the intermediate pressure refrigerant into the compression chamber 20 is performed after the pressure pulsation of the refrigerant in the muffler chamber 45 that serves as a muffler has been decreased. The side wall portion 69 of the partition member 44 is formed surrounded by the discharge chamber 58, so that the volume of the space S1 of the muffler chamber 45 is increased and the intermediate pressure refrigerant is introduced into the space S1 of the muffler chamber 45 having an increased volume. Therefore, the pressure pulsation of the refrigerant can be efficiently decreased and especially, the noise generation due to the pressure pulsation can be suppressed. Because intermediate pressure refrigerant the pressure pulsation of which has been decreased is supplied into the compression chamber 20, the operating efficiency of the compressor is improved. In a case that the refrigerant pressure in the compression chamber 20 is higher than the pressure of the intermediate pressure refrigerant in the muffler chamber 45, the check valve 46 is kept closed and supplying of the intermediate pressure refrigerant into the compression chamber 20 is not performed. Thus, the check valve 46 prevents refrigerant from flowing reversely from the compression chamber 20.

The high pressure refrigerant discharged into the discharge chamber 58 is flowed through the communication passage 74 into the discharge port 60 after flowing past the restricted passage between the projection 73 and the surface of the bottom portion 71A of the recess 71. For the purpose, the projection 73 is provided with the end thereof inserted in the recess 71 so that a clearance is formed between the end of the projection 73 and the surface of the bottom portion 71A of the recess 71 and also a gap is formed between the outer peripheral surface 73A of the projection 73 and the wall portion 71B of the recess 71. Therefore, the discharge passage extending from the discharge chamber 58 to the communication passage 74 is restricted between the projection 73 and the surface of the bottom portion 71A of the recess 71. Referring to the enlarged part in FIG. 7, the arrow line indicates the flow of refrigerant flows from the discharge chamber 58 to the communication passage 74 in the discharge passage. The pressure pulsation or the discharge pulsation of refrigerant being discharged from the discharge chamber 58 into the discharge port 60 can be decreased. Especially, there is a fear that the volume of the discharge chamber 58 is decreased and the discharge pulsation is increased because the side wall portion 69 of the discharge chamber 58 is formed so as to be surrounded by the discharge chamber 58. The discharge passage between the end of the projection 73 and the surface of the bottom portion 71A of the recess 71 is restricted, so that the discharge pulsation can be decreased.

The refrigerant discharged into the discharge port 60 is delivered through the outlet port 59 into the external refrigerant circuit. Though the volume of the discharge chamber 58 is decreased due to the structure in which the side wall portion 69 of the partition member 44 is formed surrounded by the discharge chamber 58, the decreased volume of the discharge chamber 58 can be compensated by forming the recess 72 in the valve block 15 as a part of the discharge chamber 58.

The following will describe the effects of the electric compressor 10 having the configuration described above. The side wall portion 69 of the partition member 44 is formed surrounded by the discharge chamber 58, so that the volume of the muffler chamber 45 serving as a muffler is increased. Because intermediate pressure refrigerant is introduced into the muffler chamber 45 having the increased volume, the function of the muffler chamber as a muffler can be improved and the pressure pulsation of the refrigerant can be efficiently decreased. Because intermediate pressure refrigerant with the pressure pulsation decreased is supplied into the compression chamber 20, variation of refrigerant supply amount due to the pressure pulsation can be suppressed and operating efficiency of the compressor can be improved further.

The partition member 44 includes the bottom portion 67 having the distance L1 as measured between the rear surface 8 of the valve block 15 and the outer surface of the bottom portion 67, the bottom portion 68 having the distance L2 as measured between the rear surface 8 and the outer surface of the bottom portion 68, wherein L1 is larger than L2, and the side wall portion 69 that forms the periphery of the partition member 44. The volume of the muffler chamber 45 can be easily changed by changing the distance L1 of the bottom portion 67 and the distance L2 of the bottom portion 68. For example, in the case of the partition member 76 shown in FIG. 8, wherein the distance between the rear surface 8 of the valve block 15 and the outer surface of the bottom portion 67 of the partition member 76 is smaller than the distance L1 of the bottom portion 67 of the partition member 44 of FIG. 3. In this case, the increase of the volume of the muffler chamber 45 is lessened. Thus, the distances L1, L2 can be easily changed according to the type of a vehicle on which the electric compressor 10 is to be mounted and the pressure pulsation of refrigerant introduced into the muffler chamber 45 can be adjusted. As a result, a higher degree of freedom in setting the volume of the muffler chamber 45 may be accomplished. The volume of the muffler chamber 45 can be set according to the condition of a vehicle.

In assembling the compressor 10, the valve block 15 having the muffler chamber 45, the check valve 46, and the supply port 52 is prepared and the motor housing 14, the valve block 15, and the discharge housing 16 are assembled with the valve block 15 disposed so as to form a part of the housing assembly 13 of the electric compressor 10. The valve block 15, the motor housing 14, and the discharge housing 16 are fastened together. Thus, the injection mechanism can be added easily to an existing compressor.

The projection 73 is provided with the end thereof inserted in the recess 71 so that a clearance is formed between the end of the projection 73 and the surface of the bottom portion 71A of the recess 71 and also a gap is formed between the outer peripheral surface 73A of the projection 73 and the wall portion 71B of the recess 71. Therefore, the discharge passage extending from the discharge chamber 58 to the communication passage 74 is restricted in the region between the projection 73 and the surface of the bottom portion 71A of the recess 71, so that pressure pulsation of the refrigerant being discharged from the discharge chamber 58 into the discharge port 60 can be decreased. Especially, there is a fear that the volume of the discharge chamber 58 is decreased and the discharge pulsation is increased because the side wall portion 69 of the discharge chamber 58 is formed so as to be surrounded by the discharge chamber 58. However, the discharge passage between the end of the projection 73 and the surface of the bottom portion 71A of the recess 71 is restricted, so that discharge pulsation can be decreased. Adjusting the depth of the recess 71 or the clearance between the end of the projection 73 and the surface of the bottom portion 71A of the recess 71 enables to change the above clearance.

Though the volume of the discharge chamber 58 is decreased due to the structure in which the side wall portion 69 of the partition member 44 is formed surrounded by the discharge chamber 58, the decreased volume of the discharge chamber 58 can be compensated by the recess 72 provided in the valve block 15 as a part of the discharge chamber 58, as well as the large space of the discharge chamber 58 itself.

The present invention is not limited to the above-described embodiment, but it may be modified or embodied variously within the scope of the invention as exemplified below. In the above-described embodiment, the partition member 44 has the bottom portion 67 having the larger distance L1, the bottom portion 68 having the smaller distance L2, and the side wall portion 69 that forms the periphery of the partition member 44. The shape of the partition member 44 is not limited to the above-described embodiment, but any shape may be employed as long as the side wall portion 69 of the partition member 44 is formed surrounded by the discharge chamber 58. For example, the bottom portions 67, 68 may have an inclined shape or a swollen shape like a dome. The bottom portions 67, 68 may be formed extending partially toward the discharge housing 16. In the above-described embodiment, the partition member 44 has been described as being of made of an aluminum alloy. The partition member 44 may be made of a resin or any other metal. Especially, when using a resin, intrinsic vibration frequency of the partition member 44 may be changed so as to suppress the vibration of the partition member 44 developed by the pressure pulsation of refrigerant. In the above-described embodiments, the partition member 44 is formed extending toward the discharge housing 16. As long as the muffler chamber 45 has an adequate volume and serves as a muffler adequately, the partition member 44 may be of a plate shape. In the above-described embodiment, the valve block 15 forms a part of the outer shell of the electric compressor 10, but the valve block 15 may be disposed within the motor housing 14 or in the discharge housing 16. 

What is claimed is:
 1. An electric compressor comprising: a compression mechanism having a plurality of compression chambers; an electric motor driving the compression mechanism to draw refrigerant into the compression chambers and compress the refrigerant in the compression chambers; a motor housing accommodating the electric motor and the compression mechanism, the motor housing having an injection port that communicates with one of the compression chambers, the compression chamber being in the middle of the compression; a discharge housing having a discharge chamber into which the compressed refrigerant is discharge; and an intermediate pressure housing disposed between the motor housing and the discharge housing, the intermediate pressure housing having an introduction port for introducing intermediate pressure refrigerant from an external refrigerant circuit and a communication passage that provides communication between the introduction port and the injection port of the motor housing, wherein the introduction port and the communication passage cooperate with the injection port to allow the intermediate pressure refrigerant to be injected into the compression chamber, wherein the communication passage has in the middle thereof a muffler chamber whose volume is large than volume of the communication passage other than the muffler chamber, wherein pressure of the intermediate pressure refrigerant is higher than pressure of the drawn refrigerant and lower than pressure of the compressed refrigerant discharged into the discharge chamber, wherein a partition member separates the muffler chamber and the discharge chamber.
 2. The electric compressor according to claim 1, wherein the partition member has a bottom plate and a side wall that extends from the bottom plate toward the intermediate pressure housing and is surrounded by the discharge chamber.
 3. The electric compressor according to claim 1, wherein each of the motor housing, the discharge housing and the intermediate pressure housing has a bolt fastening hole, wherein a bolt is inserted in the bolt fastening holes of the motor housing, the discharge housing and the intermediate pressure housing to fasten the motor housing, the discharge housing and the intermediate pressure housing together.
 4. The electric compressor according to claim 1, wherein a recess is formed in the intermediate pressure housing side of the discharge housing so as to expand a volume of the discharge chamber, wherein the recess partially surrounds the muffler chamber.
 5. The electric compressor according to claim 1, wherein the discharge housing has therein a projection that is formed extending toward the partition member, wherein a clearance is formed between the projection and the partition member so as to restrict flow of the compressed refrigerant from the discharge chamber to the communication passage.
 6. The electric compressor according to claim 5, wherein the projection has therein a communication passage through which an outlet port is in communication with the discharge chamber, wherein the partition member has therein a recess in which the projection is inserted, wherein the communication passage of the projection has an opening in the recess, wherein the clearance is formed between the projection and the recess of the partition member. 